[S Clark]

I'm sure your DIY diffusers are very good, although  prerecords.com/Diffusor.cfm is an empty domain- you can buy it if you want. 
Diffusers are not rocket science, but they are math based, and experience helps as well.   
As far as "the best you've found", are you saying you've actually heard or measured these  foam diffusers and found them lacking, or is this based on your assumptions.
And concerning the foam ones from Pi Audio, Dave Elledge has told me how he has measured them, how they respond at different frequencies, how different foam densities behave, how paint affects them, how backing board affects them, how spacing affects them....  in other words, real research and experience. 

[rollo]

These are the panels you're referring to?


I've had these for a couple years now without a problem. I repainted mine to match the walls.

   Yes. I was not that lucky. When up worked fine.

charles

[S Clark]

Charles is right in that the edges can be broken.  My pair is probably a dozen years old, and they get mover around a lot, placed in front of the big TV.
And yes, I've broke the tips a few times, but it's so easy to repair that it's no big deal. 
The key is they work, they won't break the bank, and good people make them.   

[clm811]

Hi.
I made my own DIY foam panels, using egg crate foam covered in a sheer fabric surrounded by a deep picture frame.
-Chas

[JLM]

In order to function diffusers must be made of non-absorbent material as they deflect sound.  Foam or sheer fabric does neither.  A better material for absorption is Owens Corning 703 high density fiberglass.  The product rollo shows is better for high frequency diffusion (if painted), but diffusion down to 1100 Hz requires 7.5 inch deep grooves (laws of physics).

[HAL]

Styrofoam is good for diffusors since it is closed cell and reflective.  Egg crate open cell foam is an absorber instead of a reflector.